#include <cstdlib>
#include <iostream>
#include <memory>
#include <utility>
#include "asio.hpp"

using asio::ip::tcp;

class session : public std::enable_shared_from_this<session>
{
public:
    session(tcp::socket socket)
        : socket_(std::move(socket))
    {
    }

    void start()
    {
        do_read();
    }

private:
    void do_read()
    {
        auto self(shared_from_this());
        socket_.async_read_some(asio::buffer(data_, max_length),
                                [this, self](std::error_code ec, std::size_t length)
        {
            if(!ec)
            {
                do_write(length);
            }
        });
    }

    void do_write(std::size_t length)
    {
        auto self(shared_from_this());
        asio::async_write(socket_, asio::buffer(data_, length),
                          [this, self](std::error_code ec, std::size_t /*length*/)
        {
            if(!ec)
            {
                do_read();
            }
        });
    }

    tcp::socket socket_;
    enum { max_length = 1024 };
    char data_[max_length];
};

class server
{
public:
    server(asio::io_context& io_context, short port)
        : acceptor_(io_context, tcp::endpoint(tcp::v4(), port))
    {
        do_accept();
    }

private:
    void do_accept()
    {
        acceptor_.async_accept(
            [this](std::error_code ec, tcp::socket socket)
        {
            if(!ec)
            {
                std::make_shared<session>(std::move(socket))->start();
            }

            do_accept();
        });
    }

    tcp::acceptor acceptor_;
};

int main(int argc, char* argv[])
{
    try
    {
        if(argc != 2)
        {
            std::cerr << "Usage: async_tcp_echo_server <port>\n";
            return 1;
        }

        asio::io_context io_context;

        server s(io_context, std::atoi(argv[1]));

        io_context.run();
    }
    catch(std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}